Remember to motivate and summarize considering the community. Provide enough information to motivate such as:

Why is this feature important?
OpenPMD standard: https://github.com/openPMD/openPMD-standard/blob/latest/STANDARD.md

It will be great to have ADIOS2's HDF5 engine output is compliant with OpenPMD for wider adoption.

What is the potential impact of this feature in the community?
HDF5 outputs created by ADIOS2 with setting engine = HDF5 could be read by openPMD compliant readers.

Is your feature request related to a problem? Please describe.
HDF5 outputs created by ADIOS2 with setting engine = HDF5 cannot be read by openPMD compliant readers because it prepends the keys with "/Step0" where 0 is the step number.

Describe the solution you'd like and potential required effort

void HDF5Common::StaticGetAdiosStepString(std::string &stepName, size_t ts)
{                                                     
    stepName = "/Step" + std::to_string(ts);
}   

Is it possible to introduce a configuration option called "openPMD_compatible" or something similar such that when it is set to true this is calculated as:

void HDF5Common::StaticGetAdiosStepString(std::string &stepName, size_t ts)
{                                                     
    if (...)
        stepName = "/data/" + std::to_string(ts) + "/";
    else
        stepName = "/Step" + std::to_string(ts);
}   

Effort seems small.

Describe alternatives you've considered and potential required effort
Alternative is to make the prefix "/Step" to be fully customizable instead of using a setting such as openPMD_compatible setting. However, this could increase the effort.

Additional context
None

Note: contents adapted from the VTK contribution guidelines